The invention relates to a radiation-sensitive semiconductor device comprising a semiconductor body in the form of a wafer having a thicker edge portion and a thinner central portion provided with a substantially flat first surface and an oppositely-arranged second surface extending substantially parallel to the first surface. The device includes a high-ohmic first region of a first conductivity type adjoining the first surface, a second region of the second opposite conductivity type which is arranged within the central portion, adjoins the first surface and forms with the first region a photodiode comprising a radiation-sensitive pn junction and is entirely surrounded by the first region within the semiconductor body, as well as a highly doped contact layer of the first conductivity type adjoining the second surface and the first region, a metal layer being formed on at least a part of the second surface, and the metal layer and the second region being provided with connection conductors, while the central portion of the semiconductor body is so thin that it is depleted at least as far as the contact layer when a voltage of less than 10 V is applied in the reverse direction across the pn junction.
The invention further relates to a method of manufacturing such a semiconductor device.
A semiconductor device of the kind described is known from the french Patent Application published under No. 2284989.
Semiconductor devices comprising photodiodes are known and are used in radiation-sensitive circuit arrangements of different kinds, for example, for optical communication, for optically recording and reading information and for various computer applications. In most cases, it is of major importance that the photodiode is fast, i.e. can follow variations of radiation intensity having a very high frequency (&gt;500 MHz).
Another important requirement is that in many cases it is desirable and even necessary that the photodiode can operate at low voltages of, for example, less than 5 V.
In order to obtain a fast photodiode, the diode capacitance should be low, which can be achieved if the diode is formed on semiconductor material of very high resistivity; However, it has been found that in most cases a slow component also occurs, which is due to diffusion of generated charge carriers from the substrate. More particularly, with high-ohmic material, in which the life of minority charge carriers is generally long, this diffusion can take place from parts located at a comparatively great depth. In the semiconductor device according to the aforementioned French Patent Application No. 2284989, the central portion is thin-etched so that this portion is already fully depleted already at a low voltage across the photodiode. Thus, a photodiode operating at a low voltage is obtained, in which in the thin central portion only the this contact layer adjoining the second surface can contribute to the aforementioned slow signal component. However, parasitic charge carriers can also diffuse to the surroundings of the photodiode form the thicker non-depleted edge portions of the wafer and thus can nevertheless give rise to a significant slow component.